Pretreatment compositions and use thereof in treating metal surfaces

ABSTRACT

Pretreatment compositions and activating process prior to the deposition of a zinc phosphate coating on the surface of iron, steel, zinc, aluminum, and alloys thereof. An aqueous colloidal solution of disodium phosphate, titanium salt, and a stabilizing agent selected from the group of alkali citrate and alkali aminopolycarboxylic acid salts is applied to the metal surface in order to activate and prepare the surface for the deposition of a fine grained microcrystalline zinc phosphate coating thereafter.

nited States Patent [191 Heller Feb.4,1975

[ PRETREATMENT COMPOSITIONS AND USE THEREOF IN TREATING METAL SURFACES [75] Inventor: Ferdinand P. Heller, Ambler, Pa.

[73] Assignee: Amchem Products, Inc.,, Ambler,

[22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,086

Related'U.S. Application Data [63] Continuation-in-part of Ser. No 95,364, Dec. 4,

1970, abandoned.

12/1948 Jernstedt 148/615 2,516,008 5 7/1950 Lum .v 148/61 OTHER PUBLICATIONS Kirk-Othmer. Encyclopedia of Chemical Technology (2nd ed.) (Vol.6) (lnterscience) (N.Y.) (1965). pages 2124. TP9-E68.

Primary E.raminerMorris Liebman AssistantExamim'rH. H. Fletcher Attorney, Agent, or Firm-Ernest G. Szoke; Howard S. Katzoff; Michael E. Zall [57] ABSTRACT Pretreatment compositions and activating process prior to the deposition of a zinc phosphate coating on the surface of iron, steel, zinc, aluminum, and alloys thereof. An aqueous colloidal solution of disodium phosphate, titanium salt, and a stabilizing agent selected from the group of alkali citrate and alkali aminopolycarboxylic acid salts is applied to the metal surface in order to activate and prepare the surface for the deposition of a fine grained microcrystalline zinc phosphate coating thereafter.

1 Claim, N0 Drawings PRETREATMENT COMPOSITIONS AND USE THEREOF IN TREATING METAL SURFACES This is a continuation-in-part of US. Pat. Application Ser. No. 95,364, filed Dec. 4, 1970, and now abandoned. v

The formation of zinc phosphate coatings can be slow and incomplete upon contact of the phosphate coating solution with the metal substrate. Should no activating or pretreating process be effected, the crystalline zinc phosphate coating deposited on the metal surface will normally be course and porous in structure.

Pretreatment and activation of the metal surface allows for accelerated formation of a subsequently applied zinc phosphate coating and permits a fine, compact, and non-porous coating to be deposited on the substrate with greatly superior corrosion-resistance. A refined zinc phosphate coating allows for a subsequently applied siccative finish possessing superior corrosion resistance and adhesive properties. A fine grained microcrystalline zinc phosphate coating is preferred under a subsequently applied paint, since a highly lustrous paint film with high corrosion resistance that is able to'withstand reverse impact without severe chipping will be formed.

Activation pretreatments which allow for accelerated formation of the coating and for enhanced quality and grain refinement of the coating are well known in the art. Such pretreatments of surfaces with aqueous activating baths containing alkali phosphates and titanium salts are disclosed, for example, in US. Pat. Nos. 2,310,239; 2,322;349; 2,456,947; 2,462,196; 2,490,062; 2,516,008; and 2,874,081. Pretreatments with solutions consisting of alkali phosphates and ferric ion are disclosed, for example, in US Pat. Nos. 2,331,196 and 2,342,738.

A pretreating composition consisting of a dialkali phosphate and a titanium salt, tends to lose its activating effectiveness after 'a short period of time. In some of the pretreatment processes to which reference has been made, certain additives are included in the activating pretreatment for the purpose of stabilizing the pretreating composition. In US. Pat. No. 2,456,947 an amine soap is added to the pretreatment composition in order to stabilize the activating material and this additive allows for cleaning and activation to be effected simultaneously. In U.S. Pat. No. 2,331,196 an activating solution containing the complex reaction product of dialkali phosphate, ferric ion, and an organic hydroxy acid is disclosed. This complex reaction product is said to prolong the life and uniform results obtained with the activating solution. An important limitation placed on this activating solution is that when the water which is employed to prepare the solution contains magnesium, calcium, and other alkaline earth cations in concentrations above 0.001% or ppm, the activating process is impeded by the presence of these cations.

In US. Pat. No. 2,516,008 a composition for simultaneously cleaning and activating a metal surface is disclosed consisting of dialkali orthophosphate, an activating compound of a metal selected from the group of titanium, zirconium, lead, and tin, an organic acid having a carboxyl group attached directly to an aliphatic group, and an alkaline cleaning composition. The organic acid is present in this composition to stabilize the composition at elevated temperatures which are necessary for cleaning to be effected. The organic acid can be present in an amount up to 50% of the weight of the activating composition, i.e., the dialkali phosphate and activating metal salt. This cleaning and activating composition, when added to water, will operate effectively ata pH of 10 to 12.5.

The pretreatments to which reference has been made tend to become more acid as the pretreatment process continues. As the pH decreases, a loss in stability can be observed and a breakdown of the activating composition occurs. This loss in stability and in the colloidal properties of the composition results in little activation thereby causing a loss in refinement of the subsequently applied zinc phosphate coating.

A presistent problem with pretreating processes and compositions consisting of dialkali phosphate and a colloidal titanium salt occurs when the composition is added to an untreated commercial water supply where metal cations such as magnesium and calcium have not been removed. The colloidal suspension will tend to deteriorate in untreated commercial water supplies and a loss of activation effect will be exhibited, thereby resulting in an unrefined zinc phosphate coating. The colloidal properties of the activating aqueous composition will be lost in a very short period of time and the rapid settling of a precipitate is observable. When an untreated, commercial water supply is utilized, it is necessary to replace the pretreating composition quite frequently so that a fixed amount of effective colloid is present. In addition, the suspension will require constant stirring and agitation to prevent the settling effect which will ordinarily result due to the deterioration of the colloid. It is undesirable and quite costly to constantly replace the pretreating composition and to constantly agitate the aqueous composition.

An added problem which prior art activation pretreatments have not remedied are the visible light and dark areas which are found on the metal surface after a phosphate coating has been deposited. These light and dark areas may remain visible after a siccative finish has been appled to the surface.

1 have discovered that the combination of a stabilizing agent selected from the group consisting of alkali citrate salts and alali metal salts of aminopolycarboxylic acids, and an activating composition consisting of a disodium orthophosphate titanium salt composition, when employed to prepare the activating bath, will prolong the life of the aqueous activating colloidal solution, and increase its capability for producing good grain refining. Most importantly, the activating composition will retain its colloidal properties when employed along with untreated commercial water supplies or with hard water containing a high content of magnesium, calcium, and other undesirable alkaline earth metal cations.

It is an object of this invention to provide an activating process employing a stable colloidal solution which does not require constant replenishment and continuous agitation during the operation of the process.

Another object of this invention is to provide an activating process employing an activating composition which will form a stable colloidal solution for prolonged periods of time in untreated water supplies containing relatively high concentrations of undesirable alkaline earth metal cations.

Another object of this invention is to provide an activating pretreatment process which allows a subsequently applied fine, uniform, and non-porous zinc phosphate coatings to be deposited on a metal surface in a short period of time.

A concomitant object of this invention is to provide a pretreating process capable of producing grain refined zinc phosphate coatings.

l have discovered an activating pretreatment process for iron, steel, zinc, and aluminum surfaces prior to the deposition of a zince phosphate coating on the substrate, wherein the aqueous activating colloidal solution employed in said process exhibits a high degree of stability. ln one aspect of this invention. the activating bath employed in the process of the present invention is prepared by the addition to water of a dry admixture consisting of an activating composition and a stabilizing agent selected from the group of alkali citrate salts or alkali metal salts of an amino-polycarboxylic acid, to form a stable colloidal solution. A metal surface activated with this aqueous activating colloidal solution and thereafter treated with a conventional phosphate coating solution wll rapidly acquire a fine grained, uniform microcrystalline phosphate coating thereon.

When I speak of the aqueous activating colloidal suspension or aqueous actiating colloidal solution," I mean the aqueous activating or activating bath containing certain polymolecular or complex particles which are finely divided and colloidally dispersed in the liquid and which possess a certain stability resulting in no settling or precipitation.

It should be understood that by activating composition, I mean the combination of disodium phosphate and titanium salt, commonly known in the art as a Jernstedt salt. This activating composition can be prepared employing well known techniques in the art. A typical method for preparing the disodium orthophosphate-titanium salt composition is presented in Example 1.

EXAMPLE 1 Titanium potassium fluoride was employed in this procedure as the source for titanium. 391 grams of disodium orthophosphate was added to 1 liter of water at a temperature of 200F. with constant stirring. 20.6 grams of titanium potassium fluoride was added and the mix was continually heated and stirred until the mass was evaporated to dryness. The residue was then finely ground. The dried residue was ready for admixing with the dry stabilizing agent in order to be employed in the aqueous activating colloidal solution of the present invention.

Typical examples of titanium salts which can be employed in the activating composition of the present invention are titanium potassium oxalate, titanium potassium fluoride. titanyl chloride and titanyl sulfate. The prefered source for titanium in the activating composition, which allows for a high degree of bath stability and acceptable activation to be obtained, is titanium potassium fluoride.

There should be sufficient titanium salt in the dry activating composition so that from 0.005% to by weight of titanium is present therein based on the combined weight of the titanium salt and disodium phosphate. The concentration of titanium, present as a compound in the resulting activating colloidal solution, can be from 0.0005 grams/liter to 0.5 grams/liter.

Disodium orthophosphate must be employed in the activating composition and should comprise at least 80% by weight of said composition. The disodium orthophosphate must be present in the aqueous activating colloidal solution in concentrations of at least 0025 grams/liter.

A surprising feature of the present invention is the operative concentration range of the activating composition in the activating colloidal solution. The high degree of stability of the activating solution allows activation to be accomplished at lower concentrations than ordinarily expected. The present process can be effected employing an activating colloidal solution wherein the concentration of the activating composition is 0.005% by weight and the titanium concentration is as low as 0.00005% by weight. The percentages given refer to percent by weight based on the total weight of the solution including the water.

During the operation of the pretreating process of the present invention, the stable colloidal suspension does not require constant stirring and agitation to maintain its colloidal and activating properties. The aqueous colloidal suspension has exceptionally long vat life and can be employed for long periods of time to activate metal surface causing the subsequently applied zinc phosphate coating solution to impart highly desirable uniform, microcrystalline phosphate coatings on the metal surface. The stability and longer vat life allows for utilization of-the activating bath in a closed circuit recirculating system for long periods of time, with little replenishment necessary and no constant overflow of the activating bath, thereby eliminating the continuous waste disposal problem.

The aqueous colloidal suspension employed in the process of the present invention consists essentially of an activating composition, a stabilizing agent selected from the group consisting of alkali citrate salts or alkali metal salts of an aminopolycarboxylic acid, and sufficient water to make an activating bath of desired activating strength. The activating composition, i.e. disodium orthophosphate-titanium salt composition, should be present in the aqueous colloidal suspension in an amount from about 0.05 grams/liter to about 30 grams/liter corresponding to from about 0.005% to about 3% by weight of said suspension and the stabilizing agent should be present in an amount such that for each part of activating composition present by weight from about 2 to about 30 parts by weight of stabilizing agent is present.

Any conveniently available alkali citrate salt can be employed in the present process so long as it is present in the amount specified herein. By alkali citrate, I mean any alkali metal or ammonium citrate salt. The alkaline citrate salts which are preferred in the operation of the activating process are diammonium citrate and trisodium citrate.

Examples of the alkali metal salts of aminopolycarboxylic acids which can be employed are alkali salts of nitrilo triacetic acid, diethylene triamine penta-acetic acid, and ethylene diamine tetraacetic acid. Tetrasodium ethylenediamine-tetraacetate, commonly known as tetrasodium EDTA, is the preferred aminopolycarboxylic acid salt to be employed in the activating process, due to its availability and the prolonged stability of the colloidal solution obtained with its use.

Similar results, as far as colloidal stability and retinement of the subsequently applied phosphate coating, will be obtained when either an alkali citrate salt or an alkali metal salt of an aminopolycarboxylic acid is employed as a constituent in the aqueous activating colloidal solution. It is preferable that one or the other of these constituents be employed during the operation of the activating process. However, the concurrent use of both an alkali citrate salt and alkali metal salt of an aminopolycarboxylic acid is not precluded so long as, when taken together, they are added and are present in the activating bath in the amounts specified herein.

The activating composition and alkali citrate salt or alkali salt of an aminopolycarboxylic acid can be added to a conveniently available commercial water supply to form the aqueous colloidal solution. The metal ions found in the usual commercial water supplies accounts for the presence of some undesirable cations, such as magnesium or calcium ions. When these cations are present in concentrations above 100 ppm, wherein the water is commonly referred to as hard water, they must be taken into account as a disruptive factor to an activating process. 1 have found that'a distinct advantage of the process of the present invention is that the water to which the constituents of the activating bath are added does not have to be treated to eliminate these cations prior to preparation of the activating colloid even when these cations are present in concentrations above 100 ppm. So long as the stabilizing agent and activating composition are present in the proportions and amounts specified herein, no prior treatment of the water employed is necessary and a stable colloidal suspension will be formed requiring no agitation and little replenishment over long periods of time, even where the undesirable metal cations are present in water hardness concentrations up to 400 ppm, as calcium carbonate.

The exact mechanisms by which the process of the present invention prevents the deterioration of the colloidal suspension in untreated water supplies is unknown. It has been postulated that the activating composition when added to water consists of an activating titanium complex and that a breakdown in this complex is caused by the undesirable metal cations found in most untreated water supplies which in turn causes a deterioration of the colloidal properties and stability of the aqueous treating bath and the loss of its activating effect. The deterioration of the colloidal properties is .usually accompanied by the formation of a precipitate due to flocculation into particles of such size that rapid settling occurs. lt is thought that the stabilizing agent employed'in the process of the present invention presents the disruption of the essential activating titanium complex, allowing for a high degree of stability and prolonged life for the aqueous colloidal solution.

The pH limit'of the present process precludes the use of citric acid in place of its corresponding alkali citrate salt. I have found that the colloidal properties of the activating bath will deteriorate quickly below a pH of 5.0. This factor makes the use of citric acid undesirable as a source for citrate in the process of the present invention. The amounts of stabilizing agent necessary herein would require that the acid be added in sufficient quantities to cause the pH of the pretreating bath to fall below 5.0 making its use disruptive. The pH limitation also precludes the use of an aminopolycarboxylic acid in place of its corresponding alkali metal salt. The amounts of acid required to be added for the process of the present invention to be operative would cause the activating bath pH to fall below 5.0 during continuous operation of the process. By employing an alkali metal salt of the acid, the required amounts of salt can be added without approaching the critical pH limit.

A unique feature of the present invention is the relatively wide pH range within which the activating process can be operated. The pH of the aqueous activating colloidal solution can be from 5.0 to about 10.0. This wide pH range, which includes slightly acid baths, makes it possible to pretreat a metal surface which has been acid cleaned and rinsed before activation. The rinse, following acid cleaning or pickling, tends to become more acid with time and as the rinsing continues the rinse is invariably carried into the activating bath by the metal workpieces. Also, in commercial operations a defective spray nozzle in the subsequent acidic zinc phosphate coating bath can cause undesirable back spray into the activating bath thereby causing the activating bath to become more acid. The pH range within which the present process can operate allows the activating bath to remain operative regardless of rinse carry over or phosphate coating solution back spray.

The stability of the activating colloidal suspension is critically dependent on the amounts of alkali metal salt of the aminopolycarboxylic acid or alkali citrate salt and activating composition present. The process of the present invention will not be effective unless stabilizing agent and activating compositions are present in the ratios specified herein.

1 have found that, on a weight basis, the concentration of alkali citrate present in the aqueous activating colloidal solution must be at least twice that of the disodium phosphate plus titanium salt present, and not more than 30 times that of the disodium phosphate plus titanium salt. For optimum stability to be obtained, when the activating composition is present in the solution in concentrations from about 0.05 grams/liter to 0.5 grams/liter, the ratio by weight of alkali citrate to activating composition should be from about 10:1 to about 30:1. Should the activating composition be present in amounts above 0.5 grams/liter, then for optimum stability to be obtained the ratio by weight of alkali citrate to activating composition should be from about 2:1 to about 20:1.

Should an aminopolycarboxylic acid salt be employed as the stabilizing agent, on a weight basis, the concentration of the acid salt present in the aqueous activating colloidal solution must be at least twice that of the dialkali phosphate plus titanium salt present. The

- ratio by weight of aminopolycarboxylic acid salt to activating composition in the activating bath should be from about 2:1 to about 30: 1. l have found that for prolonged stability of the aqueous colloidal solution to be obtained the preferred ratio by weight of aminopolycarboxylic acid salt to activating composition should be from about 2:1 to about 15:l.

Once the activating composition is prepared as specifled heretofore, it can be added to the dry stabilizing agent, i.e. alkali citrate salt or alkali metal salt of the aminopolycarboxylic acid, whereupon this dry admixture is ground and pulverized. The stabilizing agent and the activating composition are mixed in the proportions desired within the limits specified herein. The dry admixture is then added to water to produce the stable aqueouscolloidal solution with desired concentrations of activating composition, and stabilizing agent therein. I have found that the activating composition and stabilizing agent must be present in an amount, when taken together, from about 0.15 grams/liter to about grams/liter in the resulting aqueous colloidal solution. In the preferred embodiment of the present invention, the activating composition and stabilizing agent should be mixed and added concurrently to water in the manner prescribed herein. l have found that when the dry activating composition is added to water followed by the addition of the dry stabilizing agent, the colloidal solution does not possess the same degree of stability and the complex particles which are colloidally dispersed are not as finely divided.

A surprising aspect of the present invention is that a dry composite residue, prepared by incorporating the stabilizing agent with the disodium orthophosphate and titanium salt in water and evaporating to dryness, can be employed in the aqueous activating colloidal solution with no resulting loss in stability. The reason for this exceptional result is unknown. It is thought that as the disodium orthophosphate, titanium salt, and stabilizing agent are incorporated in water and evaporated to a dried residue, there is created a dry composition consisting of an intimate mixture of the colloidal titanium complex crystals and the stabilizing agent. As this dry composition is added to water to form the aqueous activating colloidal solution, the stabilizing agent is free to prevent the disruption of the essential colloidal complex.

It will be appreciated that the aqueous activating colloidal solution employed in the present process can be prepared by two alternative routes. As heretofore provided, in the preferred embodiment of this invention the activating solution is prepared by the addition to water of a dry composition comprising an admixture of the dry stabilizing agent and dry activating composition.

Alternatively, the aqueous activating bath can be prepared through the addition to water of a dry composite residue, formed by the incorporation of disodium orthophosphate, titanium salt, and stabilizing agent in water with continual heating above 200F. and stirring until evaporation to a dried residue. Sufficient titanium salt should be employed in this method of preparation so that, based on the combined weight of the titanium salt and disodium orthophosphate, there is present from 0.005% to 20% by weight of titanium. The disodium orthophosphate should be present in an amount of at least 80% by weight, based on the combined weight of titanium salt and disodium orthophosphate. The stabilizing agent, i.e. alkali citrate or alkali aminopolycarboxylic acid salt, should be present in an amount such that for each part by weight of disodium orthophosphate plus titanium salt present there is from about 2 to about 30 parts by weight of stabilizing agent present. The dried composite residue should be present in the aqueous activating colloidal solution in an amount from about 0.15 grams/liter to about 100 grams/liter.

As an aid in assuring thorough wetting of the metallic surface during treatment, it is sometimes preferable to incorporate into the aqueous activating solution a small quantity of a wetting agent, such as between about 0.005% to about 0.05% by weight. Use of wetting agents is preferred practice where the metallic surface to be treated is not thoroughly cleaned, since such agents permit wetting of the metallic substrate with removal of some or all of the contaminants present thereon. Preferably non-ionic or anionic type wetting agents are used as they provide satisfactory degrees of wetting when incorporated into the activating composition. Examples of classes of wetting agents that can be utilized are ethoxylated alkylphenols. ethoxylated alcohols, aliphatic polyethers, and alkyl aryl polyethers.

' The improved process of the present invention is normally employed after cleaning of the metal surface has been accomplished. The cleaning steps can be carried out by conventional methods which form no part of the present invention. A conventional alkaline cleaner or acid cleaner can be employed followed by a water rinse. Should the surface be heavily soiled, a detergent cleaner additive may be employed in the cleaning step. Should there be any rust deposited on the metal surface, an acid pickling step may be necessary followed by a clean, overflowing water rinse. A distinct advantage of the present invention over prior art processes is that the process of the present invention provides a stable aqueous activating colloid which is effective in preparing the metal surface for the deposition of a fine grained, microcrystalline zinc phosphate coating even though the metal was previously cleaned in a strongly alkaline solution or pickled in a strong acid.

The aqueous activating colloidal suspension of the present invention can be applied to various metal surfaces. Particularly iron, steel, zinc, and aluminum surfaces and alloys in which they form the predominant constituent can be treated in the present process, which includes workpieces such as steel sheets, galvanized sheets, steel bars and rods, aluminum sheets, and electroplated zinc surfaces.

Subsequent to pretreatment, a zinc phosphate coating solution is applied to the metal surface for a period sufficient to allow a finely crystalline uniform coating to be deposited thereon. Typical examles of commonly practiced processes and coating compositions, as are known to those in the art, by which zinc phosphate coatings will be formed on the metal surface are found in US. Pat. Nos. 3,333,988; 3,297,494; and 3,109,757, which are incorporated herein by reference.

Formula I is an example of a suitable concentrate which can be diluted to desired strength with water and is employed to treat iron, steel, aluminum, and zinc surfaces subsequent to their treatment with the activating process of the present invention.

Following the application of the zinc phosphate coating solution, the coated surface can be rinsed with water or a conventional acidulated final rinse and then dried. The rinse is necessary to remove any soluble salts which have deposited on the surface and which may interfere with a subsequently applied siccative or organic finish.

When the activation process is employed, 1 have observed a distinct reduction in visible light and dark area evident on a metal surface after the zinc phosphate coating has been deposited. This effect allows for a more visibly uniform zinc phosphate coating and a such visible surface distruptions is commercially desirable. The exact mechanism by which the present activating process reduces the light and dark areas in the zinc phosphate coatings is unknown.

The process of the present invention can be carried out employing any of hte contacting techniques known to the art. Contact can be effected by either spraying, immersion, flow-coating or brushing to effectively activate the metal surface. Preferably, the aqueous colloidal suspension will be applied to the metal surface by spray or immersion methods.

I have found that the treating time for which the metal surface must be in contact with the aqueous colloidal solution need only be long enough to insure complete wetting of the surface and can be as long as minutes. Preferably, contact time between metal surface and activating colloid should range from about 30 seconds to about 1 minute.

The process of the present invention can be effected at temperatures as high as 212F. It is preferred that the aqueous colloidal suspension be applied to the metal surface at ambient temperatures, that is from about 65 to about 90F.

The examplespresented below are illustrative of this invention and are not considered as limiting for other materials and operating conditions falling within the scope of this invention that might be substituted.

EXAMPLE 2 One hundred ninety grams of disodium orthophosphate was added to 1 liter of water at a temperature of 200F. with constant stirring. grams of potassium titanium fluoride was then added and the mix was continually heated and stirred. 400 grams of trisodium citrate dihydrate was added and the aqueous mix was heated continually to2l2F. Heating and stirring continued until the mass was evaporated to dryness. The dried composite residue was finely ground and pulverized. 2.5 grams of the dry composite residue'was added to 1 liter of water to form the activating colloidal solution. The ratio by weight of trisodium citrate to disodium orthophosphate plus titanium salt in the dry .composite residue was 2:1. The titanium content of the resulting aqueous activating colloidal solution was about 0.0008% by weight or 8 ppm. The water employed to prepare the activating colloid was untreated and contained alkaline earth metal cations, as salts such as calcium carbonate, in water hardness concentrations of at least 350 ppm.

Unpolished 2 X 4 inch steel panels were cleaned with a conventional strong alkaline cleaner at 210F. for 5 minutes, then rinsed with water. The panels were then immersed in the aqueous activating colloidal solution for seconds at a pH of 7.6. Prior to application, the activating solution had been allowed to stand for 96 hours, without replenishment or agitation. After this time period had elapsed, it will possessed its colloidal properties.

Following application of the activating colloidal solution the panels were immersed in a zinc phosphate coating solution. The following zinc phosphate concentrated solution was employed in this procedure.

% By Weight Zinc oxide Nitric acid (38 Be) 26 H,-,PO solution) 29 Ferrous phosphate l Water 29 The coating bath was prepared by adding 3.5 gallons of the concentrated zinc phosphate coating solution to gallons of water. In addition, 0.21 lbs. of sodium nitrite was added to the coating solution in order to oxidize excess ferrous ion. The panels were immersed in the aqueous acidic coating solution for 4 minutes at F. The panels were then rinsed with water and dried.

Controls were employed to compare the refining of the applied phosphate coating. The controls were processed in the same manner as the test panels, except for the exclusion of the activating process in their treatment. The control panels were cleaned, rinsed, coated with the zinc phosphate coating solution, rinsed and dried.

The panels were examined under a microscope at a magnification of 150. The control panels possessed coarse grained phosphate coatings. The panels which had been immersed in the activating colloidal solution prior to phosphate coating displayed fine grained phosphate coatings.

EXAMPLE 3 Unpolished 2 X 4inch steel panels were cleaned with a conventional strong alkaline cleaner at 210F. for 5 minutes then rinsed with water. The panels were then immersed in an aqueous activating colloidal solution for l5 seconds at a pH of 5.8. The activating bath was prepared by adding to water 1.05 grams/liter of a dry admixture consisting of diammonium citrate and the activating composition, i.e. disodium phosphatepotassium titanium fluoride composition.

The dry alkali citrate and dry activating composition had been thoroughly mixed and finely ground prior to use. The dry activating composition contained 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate. The ratio by weight of diammonium citrate to activating composition in the dry admixture was 2011. The aqueous activating colloidal solution consisted essentially of 0.1% by weight diammonium citrate and 0.005% by weight of the activating composition. The titanium content of the aqueous colloidal solution was 0.00005% or 0.5 ppm.

The water employed to prepare the activating colloid was untreated and contained alkaline earth metal cations as salts such as calcium carbonate, in water hardness concentrations of at least 350 ppm.

Prior to application the activating colloidal suspension had been allowed'to stand for 18 hours without replenishment or agitation. When applied to the panels it still possessed its colloidal properties.

A zinc phosphate coating solution was applied to the panels after the activation step had been completed.

The following zinc phosphate concentrated solution was added to water and applied to the panels.

Zinc oxide 15 HNO (38 Be) 26 H PO (757:) 29 Ferrous Phosphate 1 Water 29 The coating bath was prepared by adding 3.5 gallons of concentrate to 100 gallons water. In addition, 0.2 lbs. of sodium nitrite was added to the coating solution in order to oxidize excess ferrous ion. The panels were immersed in the aqueous acidic coating solution for 4 minutes at 170F. The panels were then rinsed with water and dried.

Control panels were employed to compare the refining ofthe applied phosphate coating. The controls were processed in the same manner as the test panels, except for the activation process which was excluded in their treatment. The controls were cleaned, rinsed, coated wi th the zinc phosphate coating solution, rinsed and dried.

The activated panels and the control panels were examined under a microscope at a magnification of 150. The control panels possessed coarse grained and porous coatings. The activated panels displayed excellent fine grained phosphate coatings.

EXAMPLE 4 Unpolished 2 X 4inch steel panels were cleaned with a conventional strong alkaline cleaner then rinsed with water. The panels were then immersed in an aqueous colloidal solution for 15 seconds at a pH of 7.7. The activating colloidal solution was prepared by adding to 1 liter of water 21 grams of a dry admixture consisting of trisodium citrate dihydrate and an activating composition, i.e. disodium orthophosphate-potassium titanium fluoride composition. The dry trisodium citrate and dry activating composition had been thoroughly mixed and finely ground prior to use.

The dry activating composition contained by weight of potassium titanium fluoride and 95% by weight of disodium phosphate. The ratio by weight of trisodium citrate to activating composition in the dry admixture was 20:1. The aqueous activating colloidal solution consisted essentially of .l% by weight of the activating composition and 2% by weight of trisodium citrate. The titanium content of the solution wherein the titanium was present as a compound, was 0.01 grams/liter or ppm.

The water employed to prepare the activating bath was untreated and contained alkaline earth metal cations as salts such as calcuim carbonate in water hardness concentrations of at least 350 ppm.

Prior to application the activating colloidal suspension was allowed to stand for 24 hours without replenishment or agitation. When applied to the panels it still possessed its colloidal properties.

A zinc phosphate coating solution was applied to the panels after the activation step had been completed. The following zinc phosphate concentrated solution was added to water and applied to the panels.

Zinc oxide l5 HNOJ (3 BC) 26 H PO (75%) 29 -Continued Ferrous Phosphate 1 Water 29 The coating bath was prepared by adding 3.5 gals. of concentrate to 100 gals. water. ln addition, .2 lbs. of sodium nitrite was added to the coating solution in order to oxidize excess ferrous ion. The panels were immersed in the aqueous acidic coating solution for 4 minutes at 170F. The panels were then rinsed with water and dried.

Control panels were employed to compare the refining of the applied phosphate coating. The controls were processed in the same manner as the test panels, except for the activation process which was excluded in their treatment. The controls were cleaned, rinsed, coated with the zinc phosphate coating solution, rinsed and dried.

The activated panels and control panels were examined under a microscope at a magnification of 150. The control panels possessed coarse grained, porous coatings. The activating panels displayed excellent fine grained phosphate coatings.

EXAMPLE 5 Unpolished 2 X 4inch steel panels were cleaned with a strong alkaline cleaner at 210F. for 15 minutes, then were rinsed with water.

The panels were then sprayed with an aqueous activating colloidal solution for 1 minute at a pH of 7.8 and a temperature of 135F. The activating colloidal solution was prepared by adding to 1 liter of water 3 grams of a dry admixture consisting of trisodium citrate dihydrate and an activating composition, i.e. disodium orthophosp'hate-potassium titanium fluoride composition.

The dry trisodium citrate and dry activating composition had been thoroughly mixed and finely ground prior to use. The dry activating composition contained 5% by weight of potassium titanium fluoride and by weight of disodium orthophosphate. For each part by weight of activating composition in the dry admixture there were 19 parts by weight of trisodium citrate. The aqueous activating colloidal solution consisted essentially of 0.015% by weight of the activating composition and 0.285% by weight of trisodium citrate. The titanium content of said solution was 0.001 grams/liter or 1.5 ppm.

The water employed to prepare the activating colloid was untreated and contained alkaline earth metal cations, as salts such as calcium carbonate, in water hardness concentrations of at least ppm.

Prior to application, the activating colloidal suspension was allowed to stand for 2 hours without agitation or replenishment. lt possessed its colloidal stability when application was effected.

Subsequent to the activating pretreatment, the panels were treated with a zinc phosphate coating solution. The following zinc phosphate concentrated coating solution was added to water and applied to the metal surface.

/1 by weight Zinc oxide 12.51

-Continued by weight 75% phosphoric acid 58.14 Nickelous oxide 1.12 Ferric chloridehexahydrate .19 Sodium chlorate 3.85 Water 24.19

The coating bath was prepared by adding 1 gal. of concentrated solution to 100 gallons of water. In addition, 0.1 lb. of sodium nitrite was added to the bath in order to oxidize any excess ferrous ion in the coating solution.

The panels were sprayed with the aqueous acidic coating solution for 1 minute at 125F. The panels were then rinsed with water and dried.

The activated metal surfaces were examined under a microscope at a magnification of 150 and were found to possess finely grained phosphate coatings;

EXAMPLE 6 Unpolished2 X 4 inch steel panels were cleaned with a conventional strong alkaline cleaner, then were rinsed with water. The panels were immersed in an aqueous activating colloidal solution for seconds at a pH of 5.0. The activating colloidal solution was prepared by the addition to 1 liter of water 1.8 grams of a dry admixture consisting of tetrasodium ethylenediamine tetraacetate and an activating composition, i.e. disodium orthophosphate and potassium titanium fluoride. This dry admixture had been thoroughly mixed and finely ground prior to use. The dry activating composition consisted of 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate.

For each part by weight of the activating composition in the dry mixture, there were 8 parts by weight of tetrasodium EDTA. The aqueous activating colloidal solution consisted essentially of 0.02% by weight of the activating composition and 0.16% by weight of tetrasodium EDTA. The titanium content of the aqueous colloidal solution was 2 ppm.

The water employed to prepare the activating colloid was untreated and contained alkaline earth metal cations, as salts such as calcium carbonate, in water hard ness concentrations of at least 350 ppm.

Prior to application, the activating colloidal suspension was allowed to stand for 24 hours without replenishment. 1t possessed its colloidal stability when appliby weight Zinc oxide 12.51 75% phosphoric acid 58.14 Nickelous oxide 1.12 Ferric chloridehexahydrate .19 Sodium chlorate 3.85 Water 24.19

14 The coating bath was prepared by adding 1 gallon of concentrated solution to gallons of water. In addition, .1 lbs. of sodium nitrite was added to the bath in order to oxidize any excess ferrous ion in the coating solution.

The panels were sprayed with the aqueous acidic coating solution for 1 minute at F. The panels were then rinsed with water and dried.

The activated metal surfaces were examined under a microscope at a magnification of and were found to possess finely grained phosphate coatings.

EXAMPLE 7 Unpolished 2 X 4 inch steel panels were cleaned with a conventional strong alkaline cleaner at 205F for five minutes and then rinsed with water. The panels were then immersed in treating solutions prepared as specified hereinbelow:

a. To 1 liter of water was added 1 gram ofa dry activating composition containing 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate. The resulting solution consisted essentially ofO. 1% by weight of the activating composition. The titanium content of the solution, wherein the titanium was present as a compound, was 0.01 grams/liter or 10 ppm. The water employed to prepare the bath was untreated and contained alkaline earth metal cations as salts, such as calcium carbonate, in water hardness concentrations of at least 350 ppm.

b. To 1 liter of water was added 2 grams of a dry admixture consisting of trisodium citrate dihydrate and an activating composition of disodium orthophosphatepotassium titanium fluoride composition. The trisodium citrate and activating composition had been thoroughly mixed and finely ground prior to use. The dry activating composition contained 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate. The ratio by weight of trisodium citrate to activating composition in the dry admixture was 1:1. The aqueous solution consisted essentially of 0.1 by weight of the activating composition and 0.1% by weight of trisodium citrate. The titanium content of the solution wherein the titanium was present as a compound was .01 grams/liter or 10 ppm. The water employed to prepare the activating bath was untreated and contained alkaline earth metal cations as salts, such as calcium carbonate in water hardness concentrations of at least 350 ppm.

c. A solution was prepared as disclosed in US. Pat.

No. 2,331,196 as follows:

Fifty-seven grams of disodium phosphate was added to 50 ml. of deionized water and 1.21 grams of ferric chloride was added to 6 mls. of deionized water The two resulting aqueous mixtures were combined and allowed to dry at 210F for 24 hours, until a dry residue had resulted through evaporation. This dry residue contained 98.5% by weight of disodium orthophosphate and 1.4% by weight of ferric chloride.

4.9 Grams of anhydrous citric acid was dissolved in 47 mls. of ethyl alcohol and then 25 grams of the disodium orthophosphate-ferric chloride residue was added thereto with thorough mixing. The mixture was then filtered and dried at F for one hour and finely ground prior to use.

The resulting admixture was employed to prepare a solution by adding 15 grams of the admixture to 1 liter of water. The water employed to prepare the activating bath was untreated and contained alkaline earth metal cations as salts, such as calcium carbonate in water hardness concentrations of at least 350 ppm.

d. The disodium orthophosphate, ferric ion, and citric acid admixture, prepared in (c) above, was employed in this procedure. 15 Grams of the admixture was added to 1 liter of deionized water.

e. The disodium orthophosphate-potassium titanium fluoride composition of (a) above was employed in this procedure. The resulting aqueous colloidal solution consisted of 0. 1 7c by weight of the activating composition. The water employed to prepare the bath was deionized water.

f. An activating colloidal solution was prepared by adding to 1 liter of water, 3.0 grams ofa dry admixture consisting of trisodium citrate dihydrate and an activating composition, i.e. disodium orthophosphate-potassium titanium fluoride. The dry trisodium citrate and dry activating composition had been thoroughly mixed and finely ground prior to use.

The dry activating composition contained 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate. The ratio by weight of trisodium citrate to activating composition in the dry admixture was :1. The titanium content of the solution was 0.0015 grams/liter or 1.5 ppm. The water employed to prepare the activating bath was untreated and contained alkaline earth metal cations in water hardness concentrations of at least 350 ppm.

g. The same activating colloidal solution was prepared as in (f) above. To this solution was added a wetting agent, such that there was .02% by weight of the wetting agent in the activating solution. The wetting agent used was an octyl phenol ethoxylate.

h. An activating and cleaning agent was prepared as disclosed in U.S. Pat. No. 2,456,947. A concentrate comprising, on a weight basis, 35.5% of kerosene, 7.2% of oleic acid, 49.8% of deionized water, 3.5% triethanolamine, and 4% disodium phosphate-potassium titanium fluoride activating composition (containing 5% by weight of potassium titanium fluoride and 95% by weight of disodium phosphate), was prepared. The oleic acid was mixed with the kerosene. The amine was dissolved in water and the oleic acid and kerosene added thereto, while rapidly stirring. The disodium phosphate-potassium titanium fluoride activating agent was mixed with water with a small amount of amine and fatty acid added to the aqueous solution. This last solution was then admixed with the already prepared emulsion cleaner. The concentrate was then added to water, such that the resultant aqueous composition comprised 2% by weight of the concentrate and 98% by weight water. The water employed to prepare the activating bath was untreated and contained alkaline earth metal cations, as salts, such as calcium carbonate in water hardness concentrations of at least 350 ppm.

i. To 1 liter of water was added 3 grams of a dry admixture consisting of tetra sodium ethylene diamine tetra acetate and an activating composition. i.e. disodium orthophosphate and potassium titanium fluoride. This dry admixture had been thoroughly mixed and finely ground prior to use. The dry activating composition consisted of 5% by weight of potassium titanium fluoride and by weight of disodium phosphate. For each part by weight of the activating composition in the dry admixture, there was l9 parts by weight of tetra sodium EDTA. The titanium content of the aqueous colloidal solution was 1.5 ppm. The water employed to prepare the activating solution was untreated and contained alkaline earth metal cations as salts, such as calcium carbonate, in water hardness concentrations of at least 350 ppm.

The panels were immersed in the respective aqueous treating baths for 30 seconds. Prior to application, the baths had been allowed to stand for about 24 hours without replenishment or agitation.

Subsequent to treatment of the panels with the pretreatments specified above, the panels were immersed in a zinc phosphate coating solution. The following zinc phosphate concentrated solution was employed in this procedure.

The coating bath was prepared by adding 3 gallons of concentrated solution to gallons of water. In addition, 0.2 lbs. of sodium nitrite was added to the coating bath. The panels were immersed in the aqueous acidic coating solution for 5 minutes at F. The panels were then rinsed with water and dried.

The activated metal surfaces were examined under a microscope at a magnification of 300 and the grain refinement quality of the coatings was observed. The results are listed in the Table below. In addition, the coatings were weighed to determine the coating weight of the deposited phosphate coating on the surfaces.

TABLE Coating Weight Bath (mg/ft) Coating Quality a 525 Coarse Grained & Porous b 555 Coarse Grained & Porous c 534 Coarse Grained & Porous d 732 Coarse Grained & Porous e 357 Fine Grained f 334 Fine Grained g 351 Fine Grained h 589 Coarse Grained & Porous i 309 Fine Grained l. A stable aqueous colloidal solution for activating ing of alkali citrate and alkali aminopolycarboxylic acid salts, such that for each part by weight of activating composition thre is present from about 2 parts by weight to about 30 parts by weight of stabilizing agent; and

. water having undesirable alkaline earth metal cations in concentrations of at least parts per million; wherein the concentration of the activating composition plus the stabilizing agent in said solution is from about .15 grams/liter to about 100 grams/liter; and wherein the pH of said solution is fro 5.0 to 10.0. 

